Localization of sources with a frequency-hopped signaling sensor array

In this paper, we present a different approach to the problem of estimating the angle of arrivals (AOA's) of D targets in Frequency - Hopped signaling sensors array for active systems, with D smaller than the number of sensor elements, L . This method is based on the application of the Maximum Likelihood Estimator for a new proposed model of received data available in different channels . The simulation results show that this approach improves the resolution in the estimation of the angle of arrivals compared wit h Monotone-Frequency signaling case. Its drawback, however, is that when the Signal-to-Noise Ratio, SNR, is low the performanc e deteriorates and a large number of snapshots is required .Dans cet article, nous présentons une méthode pour la résolution du problème d'estimation des angles d'arrivée de D cibles, par un réseau de L capteurs, où D < L, pour les systèmes actifs émettant des signaux codés en « Frequency Hopped ». Cette méthode est basée sur l'application de l'estimateur du maximum de vraisemblance à un nouveau modèle de données reçues sur différents canaux. Les résultats de simulation montrent que cette approche améliore la résolution des angles d'arrivée des cibles, comparativement à celle de la fréquence monotone. Cependant, quand le rapport signal sur bruit (Signal to Noise Ratio, SNR) est faible, la performance se dégrade et nécessite donc un nombre d'échantillons plus élevé

Carbon-poor stellar cores as supernova progenitors

Exploring stellar models which ignite carbon off-center (in the mass range of about 1.05 - 1.25 Msun, depending on the carbon mass fraction) we find that they may present an interesting SN I progenitor scenario, since whereas in the standard scenario runaway always takes place at the same density of about 2 X 10^9 gr/cm^3, in our case, due to the small amount of carbon ignited, we get a whole range of densities from 1 X 10^9 up to 6 X 10^9 gr/cm^3. These results could contribute in resolving the emerging recognition that at least some diversity among SNe I exists, since runaway at various central densities is expected to yield various outcomes in terms of the velocities and composition of the ejecta, which should be modeled and compared to observations.Comment: 49 pages, 20 figure

Nucleosynthesis in Type II Supernovae

Presupernova evolution and explosive nucleosynthesis in massive stars for main-sequence masses from 13 $M_\odot$ to 70 $M_\odot$ are calculated. We examine the dependence of the supernova yields on the stellar mass, ^{12}C(\alpha, \gamma) ^{16}O} rate, and explosion energy. The supernova yields integrated over the initial mass function are compared with the solar abundances.Comment: 1 Page Latex source, 10 PostScript figures, to appear in Nuclear Physics A, Vol. A616 (1997

A critical period for auditory thalamocortical connectivity.

1 1 8 9 a r t I C l e S Neural circuits are shaped by experience during periods of heightened brain plasticity in early life 1,2 . Children raised in an English-speaking environment easily distinguish between the phonemes /la/ and /ra/, whereas those growing up in Japan find it increasingly difficult 3 . Passive exposure of young rodents to a variety of sound features reveals a cascading series of developmental windows that open and close shortly after hearing onset to define the persistent and specific influences of early experience on the functional organization of auditory cortex Motivated by the well known binocular interactions shaped by experience in developing visual cortex 7-9 , we used in vivo neurophysiological recordings to determine whether mouse A1 also exhibits a critical period for tonotopic map plasticity induced through passive tone exposure, and whether such plasticity is present in the auditory thalamus (ventral medial geniculate body, MGBv). We then isolated the connection between MGBv and primary auditory cortex (A1) (ref. 10) in an acute brain slice preparation 11 and used voltage-sensitive dye imaging (VSDI) techniques in vitro. We mapped A1 responses to electrical stimulation of discrete sites in MGBv across early postnatal days (P8-20), following tone-rearing or gene manipulation. Our results reveal a critical period for acoustically driven topographic plasticity at thalamocortical connections in mouse A1. RESULTS Tone exposure modifies tonotopic maps in A1, but not MGBv The auditory system is tonotopically organized 10 such that tones of similar frequency activate neighboring neurons at each station along the pathway. Given that rats show experience-dependent tonotopic map reorganization following passive tone exposure during the second postnatal week 2,12 , we first used high-density in vivo mapping to delineate A1 tonotopy in young adult mice 13 that were reared either in typical acoustic environments To determine whether remapping in A1 could be explained by a shifted frequency representation in the principal subcortical input source, we also examined best frequency distributions in the MGBv. We inserted a multichannel silicon probe at an angle that matched the plane of section used in subsequent thalamocortical slice experiment

First Steps Towards Gamification Of Online Physics And Mathematics Assignments

The objective of this practice paper is to describe and analyse the use of online learning tasks on engineering mathematics and physics courses. The development of learning tasks was inspired by the promising effects of gamification techniques in higher education. Hence, some gamification elements, such as bonus points and immediate feedback were integrated into the learning tasks. Course results and student feedback demonstrate the positive impact of gamification of online learning tasks on students’ motivation and learning. In the end, further possibilities of increasing the number and repertoire of gamification techniques in engineering mathematics and physics courses are discussed

Using AMANHI-ACT cohorts for external validation of Iowa new-born metabolic profiles based models for postnatal gestational age estimation

Background: Globally, 15 million infants are born preterm and another 23.2 million infants are born small for gestational age (SGA). Determining burden of preterm and SGA births, is essential for effective planning, modification of health policies and targeting interventions for reducing these outcomes for which accurate estimation of gestational age (GA) is crucial. Early pregnancy ultrasound measurements, last menstrual period and post-natal neonatal examinations have proven to be not feasible or inaccurate. Proposed algorithms for GA estimation in western populations, based on routine new-born screening, though promising, lack validation in developing country settings. We evaluated the hypothesis that models developed in USA, also predicted GA in cohorts of South Asia (575) and Sub-Saharan Africa (736) with same precision.Methods: Dried heel prick blood spots collected 24-72 hours after birth from 1311 new-borns, were analysed for standard metabolic screen. Regression algorithm based, GA estimates were computed from metabolic data and compared to first trimester ultrasound validated, GA estimates (gold standard).Results: Overall Algorithm (metabolites + birthweight) estimated GA to within an average deviation of 1.5 weeks. The estimated GA was within the gold standard estimate by 1 and 2 weeks for 70.5% and 90.1% new-borns respectively. Inclusion of birthweight in the metabolites model improved discriminatory ability of this method, and showed promise in identifying preterm births. Receiver operating characteristic (ROC) curve analysis estimated an area under curve of 0.86 (conservative bootstrap 95% confidence interval (CI) = 0.83 to 0.89); P \u3c 0.001) and Youden Index of 0.58 (95% CI = 0.51 to 0.64) with a corresponding sensitivity of 80.7% and specificity of 77.6%.Conclusion: Metabolic gestational age dating offers a novel means for accurate population-level gestational age estimates in LMIC settings and help preterm birth surveillance initiatives. Further research should focus on use of machine learning and newer analytic methods broader than conventional metabolic screen analytes, enabling incorporation of region-specific analytes and cord blood metabolic profiles models predicting gestational age accurately

High Latitude Radio Emission in a Sample of Edge-On Spiral Galaxies

We have mapped 16 edge-on galaxies at 20 cm using the VLA. For 5 galaxies, we could form spectral index, energy and magnetic field maps. We find that all but one galaxy show evidence for non-thermal high latitude radio continuum emission, suggesting that cosmic ray halos are common in star forming galaxies. The high latitude emission is seen over a variety of spatial scales and in discrete and/or smooth features. In general, the discrete features emanate from the disk, but estimates of CR diffusion lengths suggest that diffusion alone is insufficient to transport the particles to the high latitudes seen (> 15 kpc in one case). Thus CRs likely diffuse through low density regions and/or are assisted by other mechanisms (e.g. winds). We searched for correlations between the prevalence of high latitude radio emission and a number of other properties, including the global SFR, supernova input rate per unit star forming, and do not find clear correlations with any of these properties.Comment: 40 pages of text, 3 figures, 6 tables, and an appendix of 21 jpeg figures (which is a radio continuum catalogue of 17 galaxies). to appear in A. J. (around January 1999

Machine learning guided postnatal gestational age assessment using new-born screening metabolomic data in south Asia and sub-Saharan Africa

Background: Babies born early and/or small for gestational age in Low and Middle-income countries (LMICs) contribute substantially to global neonatal and infant mortality. Tracking this metric is critical at a population level for informed policy, advocacy, resources allocation and program evaluation and at an individual level for targeted care. Early prenatal ultrasound examination is not available in these settings, gestational age (GA) is estimated using new-born assessment, last menstrual period (LMP) recalls and birth weight, which are unreliable. Algorithms in developed settings, using metabolic screen data, provided GA estimates within 1-2 weeks of ultrasonography-based GA. We sought to leverage machine learning algorithms to improve accuracy and applicability of this approach to LMICs settings.Methods: This study uses data from AMANHI-ACT, a prospective pregnancy cohorts in Asia and Africa where early pregnancy ultrasonography estimated GA and birth weight are available and metabolite screening data in a subset of 1318 new-borns were also available. We utilized this opportunity to develop machine learning (ML) algorithms. Random Forest Regressor was used where data was randomly split into model-building and model-testing dataset. Mean absolute error (MAE) and root mean square error (RMSE) were used to evaluate performance. Bootstrap procedures were used to estimate confidence intervals (CI) for RMSE and MAE. For pre-term birth identification ROC analysis with bootstrap and exact estimation of CI for area under curve (AUC) were performed.Results: Overall model estimated GA had MAE of 5.2 days (95% CI 4.6-6.8), which was similar to performance in SGA, MAE 5.3 days (95% CI 4.6-6.2). GA was correctly estimated to within 1 week for 85.21% (95% CI 72.31-94.65). For preterm birth classification, AUC in ROC analysis was 98.1% (95% CI 96.0-99.0; p \u3c 0.001). This model performed better than Iowa regression, AUC Difference 14.4% (95% CI 5-23.7; p = 0.002).Conclusions: Machine learning algorithms and models applied to metabolomic gestational age dating offer a ladder of opportunity for providing accurate population-level gestational age estimates in LMICs settings. These findings also point to an opportunity for investigation of region-specific models, more focused feasible analyte models, and broad untargeted metabolome investigation

Effects of e−e+νee^- e^+ \nu_e Decays of Tau Neutrinos Near A Supernova

We revisit the constraints implied by SN 1987 A observations on the decay rate of a multi-MeV $\nu_\tau$ decaying into the visible channel $\nu_\tau \rightarrow e^+ e^- \nu_e$, if its lifetime is more than 10 {\it sec.}. We discuss its implication for the minimal left-right symmetric model with see-saw mechanism for neutrino masses. We also speculate on the possible formation of a ``giant Capacitor" in intergalactic space due to the decay of "neutronization" $\nu_\tau$'s and spin allignment possibility in the supernova.Comment: 29 Pages, Tex file, UMDHEP 94-4